Shipping containers are typically used to transport products on ocean going transport ships. A refrigerated container is a special type of container, which incorporates a refrigeration unit (typically installed in the front 18″ of the container) which is used to keep the contents at an assigned temperature. This temperature may be set at any point within a wide range (i.e. −10F to 60F). (In actual use, refrigeration containers are sometimes used to “heat” a product such as to prevent sensitive cargos from freezing during transport through cold climates. In any case, these are still referred to as “refrigerated containers”). The refrigerated container incorporates the refrigeration unit itself, but typically must be powered by an external source.
On board ship, this power is usually provided by the shipboard power network which is connected to the container via a heavy-duty power cable attached to the container. Once the container is taken off the ship at a port, electrical plug power is usually available to power the container in the port. Once the container is placed on a “chassis” (a trailer structure pulled behind a truck used to deliver the container from the port to its final destination), power is normally provided by a generator set (“genset”) which is temporarily bolted to either the container itself or the chassis. A genset is a large assembly typically consisting of: a diesel engine, an AC alternator (to provide power), and a fuel tank and it is designed to power the container when it moves on land. The power cable connects the container to the genset.
Often, a container is taken from the ship and held in temporary storage within a yard facility (intermodal yard). Likewise, a refrigerated container is held in temporary storage at a customer or shipper's facility until it is time to transport the container to its final destination. During these periods of temporary storage, power must be provided to the container to allow the refrigeration unit to run and keep the contents at the appropriate temperature. Often, the genset is simply left on to power the refrigeration container, even though these facilities have electrical power outlets available to power stationary containers. It is generally less expensive to utilize this local (or “shore”) power when available rather than to continually run the genset (which consumes diesel fuel).
Operationally, it often occurs that refrigerated containers are inadvertently left running on the diesel generators even while parked in temporary storage within useable distance of a shore power outlet. Thus, the operator is not utilizing the most efficient power source available.